In conventional systems for quenching workpieces, as described for example in German Patent Specification 42 18 126, the workpieces are conveyed through a quenching apparatus on a horizontally extending roller conveyor. On their path through the apparatus the workpieces have applied to them from the underside, in an arrangement designed like a steeping pot, a quenchant that flows as a liquid against the workpieces from below, flows through the gaps between the workpieces, and is then carried off upward and to the side. A corresponding pump device that allows a flow of the liquid quenchant from below is provided for these purposes.
An apparatus for achieving uniform cooling in a hardening bath is known disclosed in German Published Patent Application 21 43 536. The known apparatus comprises a vessel with coolant liquid. A conveyor belt equipped with holes is arranged in the hardening bath. The workpieces pass via a conveyor trough, under their own weight, onto the conveyor belt, are conveyed thereon initially in a horizontal direction, and are then transported obliquely upward via a rising section, out of the bath, to a delivery end.
Propellers with pivotable blades are arranged in the hardening bath. The propellers are controlled by means of a timing relay in such a way that the direction of incidence of the propeller blades changes, for example, every 5 seconds. As a result, the flow direction of the coolant liquid flow passing vertically through the conveyor belt is reversed each time, so that the coolant liquid flows alternately from top to bottom, and from bottom to top, through the conveyor belt.
The known apparatus has the disadvantage that the merely perforated conveyor belt, with its uniform motion in only one direction, results in perceptible shadowing. Consequently the workpieces to be cooled experience an inhomogeneous incident flow despite the cooling flow which reverses in the vertical direction, since portions of the workpieces are shadowed by the remaining webs in the conveyor belt. This leads to distortion phenomena on the workpieces, which are intolerable for many workpieces.
It is therefore the object of the invention to develop a method and an apparatus of the aforesaid kind in such a way that the quenching effect is further improved, and that the workpieces can be quenched without distortion.